The present invention relates to a temperature-compensated oscillation device and, more particularly, to a digitally controlled temperature-compensated oscillation device.
A digitally controlled, temperature-compensated oscillation device has been extensively used as a local oscillator of a mobile radio apparatus because its frequency generally remains stable over a wide temperature range. Such a type of oscillation device comprises a temperature sensing section including a temperature sensor and an analog-to-digital (AD) converter, a read only memory (ROM) which stores compensation data associated with outputs of the AD converter, and an oscillating section responsive to an output of the ROM and comprising a digital-to-analog (DA) converter and a voltage controlled oscillator (VCO).
The problem with an oscillation device having the above construction is that a noticeable variation in ambient temperature causes an output of the AD converter, i.e., an output value of the ROM, to vary sharply for a moment to add frequency modulation noise and phase modulation noise to an output of the VCO. In a multichannel communication system, these noises consitute a source of noise for other channels. That noise on other channels requires the exclusive frequency band to have an undesirable width.